Single-mode fiber optic transceiver connected to RX or TX

For single-mode fiber, the transceiver's TX (transmit) port should connect to the RX (receive) port of the opposite device, and vice versa.

Understanding RX and TX

• TX (Transmit): The port that sends optical signals out from the transceiver.
• RX (Receive): The port that receives incoming optical signals from the other end of the fiber link . In a fiber optic link, TX on one device must connect to RX on the other device to ensure proper signal flow. This applies to single-mode fiber (SMF) as well as multi-mode fiber, but single-mode is typically used for longer distances, often spanning 10–80 km depending on wavelength and module type .

Single-Mode Fiber Considerations

• Single-mode transceivers commonly use 1310nm (LX) or 1550nm (ZX) wavelengths.
• Typical TX power ranges for 1310nm modules are -5 to 0 dBm, with RX sensitivity down to -14 dBm; for 1550nm modules, TX can be 0 to +5 dBm, with RX sensitivity down to -24 dBm .
• Because single-mode fiber carries light over long distances, connecting TX to TX or RX to RX will result in no signal reception and potential link failure.

Practical Tips

• Always cross-connect TX to RX between devices.
• For short single-mode links, a high TX power can overwhelm the RX; use optical attenuators if necessary to prevent damage .
• Ensure fiber connectors are clean, as dust or debris can cause significant signal loss.
• Verify the transceiver specifications for TX and RX power to match the link distance and fiber type . Key Takeaway: On single-mode fiber, plug the transceiver's TX into the other device's RX and RX into the other device's TX. This ensures proper optical signal transmission and reception over long distances.